The present invention relates to the presentation of data and more particularly to providing a plurality of different file system views for the same data.
Data protection (which includes backing up computer data, restoring computer data, securing computer data, and managing computer data storage) and disaster recovery procedures are essential processes in organizations that use computers. In fact, data protection is the single most expensive storage administrative task. Most large organizations perform data backups to tape media and use a robotically controlled tape library (or tape jukebox) to assist with backup automation. Performing and managing backups and restores involves many functions including, for example, media management (including tape tracking, rotation and off-site storage), tape jukebox management, file tracking, backup scheduling, assisted or automated data restore, and data archival.
In order to effectively perform the above functions, a sophisticated data protection application (DPA) is required. Examples of such DPAs include, for example, Legato NetWorker, Veritas BackupExec and CA ArcServe. DPAs automate and assist with the essential functions of data protection. DPAs are designed specifically to work with physical tape media, tape drives and tape libraries. Most of the complexity in DPAs relates to their interaction with physical tape.
Most DPAs implement sophisticated tape packing when performing backup of data. The function of a DPA is to efficiently collect data from the system that is being backed up and then to effectively store this data on tape. DPAs, therefore, implement their own proprietary tape formats to best suit their functionality.
Restoring data backed-up on tape is an operation that is also performed via the DPA. The DPA typically presents an interface that allows a user to select the file(s) required to be retrieved and facilitates the process of restoration. Physical tapes can only be sequentially accessed and are relatively slow compared to magnetic disks. This means that there is usually a significant time penalty (several minutes) when a file is restored. The restore process is cumbersome and requires that a user learn the operation of the DPA. Restore operations can typically only be performed by a small number of system administrators at a site who have been trained on the DPA's operation.
Furthermore, the data that is stored on physical tapes is considered off-line storage. In order to access the data, it is necessary for the DPA to read the files from the tape and then create appropriate files in a disk-based file system and write the contents of the files to the disk. This indirect restore process is necessary since the seek times for tape are extremely slow compared to disk (minutes instead of milliseconds). Although it would be easier for a user to access data on tape in the same way as data on disk, this would require random access patterns to tape. Tapes, however, are sequential devices making their performance extremely limited when randomly accessed.
It would therefore be desirable for data written in a sequential format by a particular DPA to be randomly accessible with standard file system semantics at disk-like speed.